Short-tailed shearwater, Ardenna tenuirostris, trophic levels, lag, longitudinal study, seabird harvest

Environmental variations play an important role in the population dynamics of seabirds, as they influence key aspects such as survival and individual breeding success. Oscillating climatic conditions (e.g. the Pacific Decadal Oscillation [PDO] and the El Ni‚àö¬±o‚Äöv†v¿Southern Oscillation [ENSO]) dramatically alter marine productivity, both spatially and temporally. Unpredictable environmental conditions result in prey distributions that are highly variable, patchy and unpredictable, which influences the foraging behaviour of marine predators. Small changes in oceanographic conditions can adversely affect primary productivity and therefore influence seabird foraging success, including that of the short-tailed shearwater. The short-tailed shearwater (Ardenna tenuirostris, previously known as Puffinus tenuirostris) is a transhemispheric migratory seabird that breeds only in south-eastern Australia and migrates to the northern Pacific Ocean for the austral winter (Skira 1996). They are commonly known as the 'mutton bird', and their chicks are subject to annual commercial and recreational harvesting in Tasmania. The short-tailed shearwater population is fully protected and not harvested elsewhere in Australia. Currently, some short-tailed shearwater populations in south-eastern Australia are decreasing, but it is unclear what is driving this decrease. The factors influencing the population decrease may include changes to resources, in addition to, or even compounded by, the local harvesting of chicks and subsequent lower recruitment rates into the breeding population. In this study, we investigated the breeding parameters of short-tailed shearwater from four harvested colonies (study period 2010 to 2018) and one unharvested colony (study period 1950 to 2012) within the Furneaux Islands, Tasmania, Australia. The aim was to quantify the relationship between breeding parameters and large-scale climate indices in the Northern Hemisphere (i.e. Northern Pacific Index and PDO) and Southern Hemisphere (i.e. ENSO and Southern Annular Mode [SAM]). We found that breeding parameters (e.g. breeding attempts and fledging rates) were influenced by large-scale climate conditions in the preceding year, and by local conditions such as rainfall. These findings demonstrate that both large-scale climate indices (e.g. PDO, SAM) and local environmental conditions can explain some of the variability among the breeding parameters of short-tailed shearwater within colonies in the Furneaux Island Group. A feasibility study was also undertaken using a fisheries stock assessment package (i.e. C\\(^{++}\\) Algorithmic Stock Assessment Laboratory [CASAL] framework) to conduct an integrated assessment for short-tailed shearwater. We used data from a historical capture-mark-recapture program of an entire colony (100 to 200 birds) of short-tailed shearwater at Fisher Island, Furneaux Island Group, for the period 1947 to 2017, to estimate unknown population parameters and empirical data from the census (observations) to fit the model parameters (e.g. age frequency and abundance). We found this approach was appropriate for short-tailed shearwater. We also identified specific aspects of this approach that would require further work to enable the results to be used to inform management decisions. The outcomes of this study address existing knowledge gaps and improve the understanding of the factors affecting short-tailed shearwater populations. The feasibility study provides a baseline for ongoing scientific management advice to improve the sustainability of the annual harvest of short-tailed shearwater, with further studies needed to conduct a fully parameterised sustainable harvest model.